PROJECT SUMMARY/ABSTRACT Pregnancy is a unique period in which the inherent biological complexity of any single human organism is exponentially amplified by an intimate interaction between a rapidly developing fetus and an adult mother who exhibits remarkable physiological adaptations over the nine months of pregnancy. Importantly, the biological interests of the two organisms are not always congruent, reflecting conflicting metabolic interests and limited supplies. Furthermore, maternal-fetal interaction does not occur through a passive sieve, but is actively and dynamically orchestrated by the placenta, an organ with its own set of physiological needs. It is therefore apparent that any disruption of the homeostatic equilibrium among the mother, placenta, fetus or their environment may manifest as a clinical disease that challenges maternal physiology (e.g., preeclampsia) or fetal development (e.g., fetal growth restriction), or may lead to premature termination of the pregnancy (e.g., preterm birth). The intact function of the placenta includes a set of signals that are generated by placental trophoblasts and communicated to the maternal and/or the fetal compartments. These signals include hormones (proteins, glycoproteins, steroid hormones) and growth factors, which have a paracrine and endocrine effect on maternal and, possibly, fetal tissues. Our new line of research centers on nanovesicle (exosome)-based communication. These exosomes are produced in human trophoblasts and harbor signals that are germane to pregnancy health. Among these signals are placenta-specific microRNAs (miRNAs) that, we recently showed, confer viral resistance to recipient cells. These miRNAs may also impact local placental biological processes, such as trophoblast migration and invasion. While the placenta produces an abundant number of exosomes, their target tissues are currently unknown. Moreover, the mechanisms by which placental exosomes deliver their cargo to target cells and the regulation of their intracellular function have not been hitherto investigated. We therefore seek to test the hypothesis that human trophoblastic exosomes use specific uptake mechanisms to target maternal tissues, locally and distantly, and impact cell function. We will test our hypothesis using human trophoblasts and exosomes derived from pregnant women. For those experiments that cannot be performed in humans, we will use mice that have been validated as appropriately modeling the human processes under study. Ultimately, our data will illuminate previously unknown mechanisms of crucial, exosome-based communication between the feto-placental and maternal compartments. Further, as placental exosomes are accessible via the blood, data generated by our investigation will introduce new means to investigate the human placenta, and may promote the use of exosomes as part of the diagnostics of placental dysfunction and indicate new avenues for nanoparticle-based therapeutics.